This invention relates to a process for producing diisopropyl ether of high purity from isopropyl alcohol and propylene continuously with high yield.
In the prior art processes, it has been a common practice to separate and purify diisopropyl ether obtained as a by-product when isopropyl alcohol is produced by hydrating propylene. However, the following drawbacks have been encountered with those processes. First, production of diisopropyl ether is subject to restriction by the rate of formation of the by-product upon the production of isopropyl alcohol. Second, the by-product obtained is a mixture of diisopropyl ether and other substances which obstruct the separation and purification of diisopropyl ether, so that it is difficult to purify the diisopropyl ether mixture. Furthermore, where the indirect hydrating process is used in which sulfuric acid is used as a catalyst for the production of isopropyl alcohol, installations used suffer from severe corrosion.
Heretofore, a process is disclosed, for example, in U.S. Pat. No. 2,067,385 issued to Evans, in which ether is prepared from secondary base olefin and aliphatic alcohol in the presence of sulfuric acid as a catalyst. Since H.sub.2 SO.sub.4 is used as a catalyst, however, the process has been attended with the following drawbacks:
1. Installations used suffer from severe corrosion. PA1 2. Where olefin of a small carbon number such as propylene is used, there is produced an ether which is easily soluble into a layer of H.sub.2 SO.sub.4, with the result that ether thus produced is difficult to be separated from the H.sub.2 SO.sub.4. In addition, there arises the necessity of adding much water to the reaction mixture prior to the heating and isolation of ether, e.g. isopropyl ether because the direct heating of the concentrated sulfuric acid-ether mixture causes the reverse reaction in which the ether is decomposed. Thus, the H.sub.2 SO.sub.4 catalyst cannot be directly reused. For reusing the catalyst reconcentration is required. PA1 3. As a substantial quantity of waste sulfuric acid is produced in the concentration of the catalyst for recovery, water is contaminated.
Because of these drawbacks as described, it has been found that the process for synthesizing diisopropyl ether by using concentrated sulfuric acid is not practically usable.
The above-described U.S. patent teaches, besides the use of sulfuric acid, the use of catalyst in the form of solid, such as (1) phosphoric acid, esters of sulfuric acid, (2) POCl.sub.3, boron halides, AlCl.sub.3, FeCl.sub.3, (3) Al.sub.2 (SO.sub.4).sub.3, MgCl.sub.2, KHSO.sub.4, NaHSO.sub.4, potash alum, acid salt, (4) active charcoal, silica gel, kieselguhr, kaolin and aluminum silicate.
From the fact that Evans describes in page 2, left column, lines 3 through 6 of the specification that H.sub.2 SO.sub.4 is preferable as a catalyst, it will be seen that the above group (1) would not be industrially effective for the same reason as discussed above in connection with disadvantages of sulfuric acid.
The compounds of Group (2), the so-called Friedel-Crafts compounds, have a fairly high acidity so that they have similar properties to concentrated sulfuric acid as far as corrosion is concerned. These metal halides are hygroscopic and are very reactive with water so that they are decomposable due to the remaining moisture even if apparently dry. Any of the decomposition products are so corrosive as to erode every portion of the apparatus. Furthermore, as these compounds absorb moisture from the air, they are troublesome in handling and are disadvantageous in industrial application.
The compounds of Group (3) are salts which are hygroscopic and have drawbacks similar to those as mentioned above. In fact, the reactivity is not improved even if Al.sub.2 (SO.sub.4).sub.3, for example, is employed as the catalyst.
The compounds in Group (4) are solid materials similarly to the acidic cation exchange resins of the present invention. These compounds as such may be usable as a particulate material for the reaction layer of fixed bed. However, even if they are actually used for the reaction of ispropyl alcohol with propylene, it will be evident that the reaction would hardly occur or, if any be actuated with lowest activity.
In fact, the Evans patent does not teach concretely the art of producing ether of high purity efficiently by using any of these compounds in the form of a solid.
Alternatively, British Pat. No. 957,000 teaches the art of synthesizing ter-butyl-alkyl ether from isobutylene and alcohol by using a cation-exchange resin. This British patent, however, discloses only the reaction between isobutylene and alcohol at a low temperature ranging from 0.degree. to 100.degree. C., preferably from 20.degree. to 80.degree. C. What is taught by said British patent is the case where a tertiary olefin such as isobutylene is used as the olefin, rather than the case where a secondary base olefin such as propylene is employed. The British patent discloses on lines 9 through 14 at page 2 in the specification that isobutylene has a reactivity which is many times greater than the reactivity of an olefin such as propylene. Such description would be interpreted as making a denial of the use of propylene as an olefin in the production of diisopropyl alcohol on an industrial scale, rather than as implying the possibility of the use of proplyene as olefin therefor.